The majority of kids graduate at 18.
Freshman Year - 18
Sophomore Year - 19
Junior Year - 20
Senior Year - 21
If a player redshirted and took two years off for a mission they should be 24.
No opposing player should be under 18 unless they were young for their grade and no BYU player should be older than 24 without some sort of eligibility exception.
So sure, there is a difference between 17 and 25 but what does that have to do with football?